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Phenomenology of heavy-ion collisions
How can one characterize what is created in a heavy-ion collision?
Focus on “collective phenomena” present in nucleus-nucleus collisions, but absent in pp collisions (“condensed matter physics of QCD”)
Establish a reference, in which collective effects are absent.
Quantify the deviation from these benchmarks in nucleus-nucleus collisions.
Analyze the origin of these deviations.
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First measurement: multiplicity
number Nch of charged particles ∝
PHOBOS Collaboration, Phys. Rev. Lett. 85 (2000) 3100
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First measurement: multiplicity
number Nch of charged particles ∝
PHOBOS Collaboration, Phys. Rev. Lett. 85 (2000) 3100
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Nucleon-nucleon cross-section
taken from Miller, Reygers, Sanders & Steinberg, Ann. Rev. Nucl. Part. Sci. 57 (2007) 205
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Multiplicity distribution
Vary the equivalent number of nucleon-nucleon collisions between and :
Probability P (n,b) to find a multiplicity n in a particular A-B collision at impact parameter b:
Gaussian around , with some dispersion; given by a Monte-Carlo simulation.
event-multiplicity distribution:
probability that an inelastic process occur
N̄AB(b) =(
1− x
2N̄AB
part(b) + xN̄ABcoll (b)
)N̄NN
N̄ABpart(b) N̄AB
coll (b)
N̄AB(b)
dNevts
dn=
∫dbP (n,b)
{1−
[1− σinel
NNTAB(b)]AB
}
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taken from Miller, Reygers, Sanders & Steinberg, Ann. Rev. Nucl. Part. Sci. 57 (2007) 205
Multiplicity distribution
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Multiplicity distributiondNevts
dn=
∫dbP (n,b)
{1−
[1− σinel
NNTAB(b)]AB
}
figure from Kharzeev & Nardi, Phys. Lett. B 507 (2001) 121
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Multiplicity vs. geometry
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taken from Miller, Reygers, Sanders & Steinberg, Ann. Rev. Nucl. Part. Sci. 57 (2007) 205
Multiplicity vs. geometry
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taken from Miller, Reygers, Sanders & Steinberg, Ann. Rev. Nucl. Part. Sci. 57 (2007) 205
Cross-checking Glauber theoryMultiplicity at projectile rapidity vs. at midrapidity
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data from PHOBOS Collaboration Phys. Rev. C 74 (2006) 021901(R)
Pseudorapidity distributions
figure taken from Miller, Reygers, Sanders & Steinberg, Ann. Rev. Nucl. Part. Sci. 57 (2007) 205
Collision centralities: 0-6%, 6-15%, 15-25%, 25-35%, 35-45%, 45-55% (missing / not shown at the lower two energies)
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taken from BRAHMS Collaboration, Phys. Rev. Lett. 94 (2005) 162301
Rapidity distributions
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Multiplicity at mid-rapidityBeware: in fact, at η=0, not y=0!
taken from PHOBOS Collaboration Phys. Rev. C 74 (2006) 021901(R)
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data from PHOBOS Collaboration Phys. Rev. C 74 (2006) 021901(R)
Charged hadron multiplicity
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data from PHOBOS Collaboration Phys. Rev. C 74 (2006) 021901(R)
We boost everything to the rest frame of one nucleus (“projectile”)
universal
“limiting fragmentation”
Charged hadron multiplicity
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data from PHOBOS Collaboration Phys. Rev. C 74 (2006) 021901(R)
We boost everything to the rest frame of one nucleus (“projectile”)
universal
“limiting fragmentation”
ln√
sNN
growslike
Charged hadron multiplicity
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We boost everything to the rest frame of one nucleus (“projectile”)
universal
“limiting fragmentation”
Charged hadron multiplicity
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We boost everything to the rest frame of one nucleus (“projectile”)
universal
“limiting fragmentation”
−ybeam @ LHC
Charged hadron multiplicity
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We boost everything to the rest frame of one nucleus (“projectile”)
universal
“limiting fragmentation”
ln√
sNN
growslike
−ybeam @ LHC
Busza 2004; N.B. & Wiedemann 2008
Charged hadron multiplicity
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The naive extrapolation of RHIC data yields at -increase, in opposition to conventional power-law rise
dN ch
dη≈ 1100 η = 0
ln√
sNN
Charged hadron multiplicity
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The naive extrapolation of RHIC data yields at -increase, in opposition to conventional power-law rise
dN ch
dη≈ 1100 η = 0
ln√
sNN
organized byN.Armesto, N.B., S.Jeon & U.A.Wiedemann
Hijing + baryon junctions: 3500 EPOS (multiple scattering): 2500 pQCD minijets + saturation
(EKRT) of produced gluons: 2570 AMPT (Hijing+ZPC): ≈2500 Percolating strings:
DMPJET III: ≈1900 Pajares et al.: 1500-1600
2-component + shadowing: ≈1700
“Geometric scaling” (Armesto, Salgado, Wiedemann): 1700-1900 Gluon saturation (Kharzeev,
Levin, Nardi 2000-05): 1800-2100 B-K eq.+ running coupling
(Albacete, Kovchegov): ≈1400 “CGC” (Gelis, Stasto, Venugopalan):
1000-1400 ALCOR (quark-antiquark plasma
+ recombination): 1250-1830 = dN ch
dy
Charged hadron multiplicity
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taken from BRAHMS Collaboration, Phys. Rev. Lett. 93 (2004) 102301
Net baryon-number density
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bulk: “soft particles”
high-pT particles
Transverse-momentum spectrum
∝ N̄ABcoll (b)∝ N̄AB
part(b)